1. Field of the Invention
The invention relates to water heater and storage tank assemblies, and is directed more particularly to such an assembly of the heat pump type.
2. Description of the Prior Art
A widely accepted and used water heater for residential hot water production and storage is the electric resistance water heater and storage tank. Referring to FIG. 1, it will be seen that such water heaters typically include a tank 20 defining a chamber 22 for retention of water. A water inlet pipe 24 is provided with a first connection 25 for interconnection with a cold water supply line (not shown) and conveys fresh relatively cold water into the chamber 22. Electric resistance elements 26 heat the water in the tank. A hot water outlet pipe 28, provided with a second connection 29 for interconnection with a hot water discharge line (not shown), conveys relatively hot water from the chamber 22. A pressure and temperature relief valve 34 is provided at the top or side of the tank 20 and typically is connected to a pressure and temperature relief valve drain tube 36 extending downwardly alongside the tank 20. An electrical power line 30 is provided with an electrical connector 32 for connection to a power source (not shown), such as a high voltage household outlet, and provides electrical power to the electric resistance elements 26. Such electrically powered assemblies typically have an Energy Factor (a measure of efficiency) of about 0.86 for a 50 gallon tank. The assemblies are available in different sizes, usually 40-80 gallon capacity, most typically 40 or 50 gallon capacity, and are dimensioned for acceptance in residential basements, kitchens, closets, and the like. Typically, the cold water inlet and hot water outlet are disposed at the top of the tank, and the electrical power line is disposed at the top (as shown) or side of the tank.
Heat pump water heaters and storage tank assemblies are generally known in the art. In U.S. Pat. No. 2,516,094, issued Jul. 18, 1950, to A. W. Ruff, there is shown and described a heat pump water heater. In the Ruff assembly, a compressor and condenser are disposed within a water containing tank and an evaporator is disposed on top of the tank. These heat pump components occupy a large portion of the volume of the tank, leaving a limited volume for storage of water. The hot and cold water connections are on the side of the tank, the cold water inlet being near the bottom of the tank.
In U.S. Pat. No. 2,696,085, issued Dec. 6, 1954, to A. W. Ruff, there is disclosed a similar heat pump water heater differing from the '094 assembly in that the condenser portion of the refrigerant circuit comprises three sets of coils submerged high, low and midway inside the tank.
In U.S. Pat. No. 2,575,325, issued Nov. 20, 1951, to E. R. Ambrose et al, there is shown a heat pump water heater and storage tank in which a compressor and condenser are located within the tank and two evaporators are located externally of the tank.
While heat pump water heaters provide improved efficiencies over electric resistance water heaters, they have never attained wide acceptance. The reasons for the lack of acceptance appear to be (1) high initial costs; (2) the fact that water heater installers (a) are used to placement of hot water and cold water connections in about the same place relative to the tank, which typically is a 40 gallon or 50 gallon tank, and used to a single simple electrical connection, and (b) are not equipped to handle system components external to, and removed from, the tank; (3) the fact that often a water heater is located in a confined space which is constructed with enclosure of a 40 or 50 gallon residential electrical water heater of conventional shape in mind; and (4) the fact that heat pump water heaters can be slow to recover from a large draw-down of hot water.
It has been recognized by the U.S. Department of Energy that wide-spread acceptance of heat pump water heaters would lead to substantial savings in energy consumption.
There is thus a need for a heat pump water heater having substantially improved efficiencies over a comparable electric resistance water heater, having substantially the same physical characteristics as a comparable electric resistance water heater, and having connections that can easily be made by anyone practiced in installing electric resistance water heaters. There is further a need for such a heat pump water heater wherein provision is made for quick recovery from large draw-downs. There is still further a need for such a heat pump water heater which is comparable in initial cost to that of an electric resistance water heater.